In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and the drill bit are removed, and the wellbore is lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is typically filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore. Numerous operations occur in the well before or after the casing is secured in the wellbore. Many operations require the insertion of some type of instrumentation or hardware within the wellbore.
Coiled tubing is a long continuous length of spooled or “reeled” thin walled pipe that can be pushed into a wellbore. This coiled tubing can be used to conduct many different downhole operations in oil and gas wells. For example, coiled tubing can be concentrically inserted into an existing wellbore in order to clean out sand or other debris from such well. Further, conventional coiled tubing can be used to conduct downhole operations by attaching a fluid activated tool to the distal end of the tubing, and then pumping pressurized drilling fluid through the coiled tubing to actuate such tool. For example, in the case of a mud motor and drill bit, the drill bit and hydraulic mud motor are lowered into the borehole as the coiled tubing is spooled off a reel, thereby allowing the borehole to be drilled deeper into subterranean formations.
Coiled tubing is driven downhole by coiled tubing injector heads. Conventionally, coiled tubing injector heads employ motor driven endless chain loops that are supplied with carrier blocks with grippers for creating a strong friction grip against the coiled tubing. As the tubing is fed into the injector head, the gripper blocks press against the coiled tubing, which is mechanically forced into the wellbore as the endless chains of the injector head are turned. The direction of the endless chain loops is reversed to withdraw the tubing from the wellbore. The coiled tubing is conventionally introduced into the wellbore through a seal, which contains the well pressure as the coiled tubing is introduced or withdrawn.
Typically, the coiled tubing injector head is positioned above the wellhead. In workover operations for example, the injector head is often suspended above the wellbore by a crane or other device. A tubing guide may be used to connect the injector head to the wellhead (including, for example, a blowout preventer) at the top of the wellbore to prevent the coiled tubing from buckling or otherwise deforming prior to entering the wellbore.
Conventional injector heads typically utilize specially-adapted chain assemblies to grip the outer surface of the coiled tubing string. The current art requires solid carrier blocks be assembled with hundreds or even thousands of individual chain components on a single injector head. A solid carrier block that becomes worn, cracked or broken necessitates removal and/or replacement of the entire injector chain and conventional solid carrier block assembly.
Problematically, the chains of the injector head are heavy and complex. Removal of the chains for repair in the case of a broken carrier block requires effort on the part of the oil field workers, time for disassembly, time for repair, and time for re-installment. This process can keep the injector head out of commission for many hours or even days. Due to the cost of drilling operations, companies stand to lose large sums of money when an injector head's chains need to be removed for repair. Additionally, due to the heavy nature of the chains and potentially awkward positioning needed for removal and re-installment, oilfield workers are subjected to less than optimal safety conditions.
Therefore, there exists a need to avoid having to remove and disassemble entire injector chains due to one minor problem with a carrier block. The problems described above are answered by using a split carrier block of the present invention.